Really does go to show how rofly some of the legal systems are in the US. The $870m number according to some legally knowledgeable 2p2 posters is arrived at by summing the total losses of all kentucky residents from 2006-2012
not net of winnings So its every dollar that any poker player in kentucky ever wagered in that period. The actual $ rake number that PokerStars made from kentucky residents for the period was ~$18m. There is lots of legal wrangling still to do but what is worrying is that this absurd system is actually used in practice and has precedent in kentucky. For years poker players in the state have been fighting to not have to use this system in reverse on their income tax forms. Income from poker winnings cannot be netted against poker losses in the state so most just move or fudge their tax returns.
As for whether this can be appealed beyond the state level I don't know, I would assume so as AmayaStars as an entity operates in New Jersey at the moment whereas a person that resides solely in Kentucky wouldn't have recourse at the federal level.
Also apparently the appointed judge in this case was already pretty tilted with PokerStars before the sale. Mark Scheinberg was able to show the state legislature the finger for years what with the company being offshore. He ignored deposition requests, hearings and letters from state judges so now that its AmayaStars and they need to jump through the regulatory hoops to get US licences (as is essential to the growth plan that they borrowed the mountain of cash to buy 'Stars on the back of) the judge is more than happy to stick the boot in.
In saying all that, as shitty as the treatment has been from AmayaStars chopping rewards for Supernova and SNE players 11 months into a 12 month programme, if they really do get slapped with a $870m bill then its a lose for everyone. The Amaya share price slumped to 18-month lows on the news.

Edit: Image won't show for some reason, it works as a link